The present invention relates generally to measuring the speed and timing of aquatic craft, and more particularly relates to the timing of motor boats in water ski competitions and the like.
In competitive water skiing a motor boat is driven through a course of parallel buoys typically separated by a few feet (See FIG. 1). As is common in the art, there are additional parallel lines of outer buoys located on either external side of the boat's course. A skier must navigate around these outer buoys from side to side, crossing behind a moving boat, in order to circumscribe a plurality of buoys describing an approximately sinusoidal path without falling. As is well known in the art, a constant boat speed allows water skiing participants to compete on an equal basis and concomitant official records to be maintained.
As is also well known in the art, competition ski boat drivers are subject to numerous qualifications and special training to improve their driving skills. Heretofore, the method of maintaining uniform boat speed during water skiing competitions has been to time a boat's passage through its course from the first buoy to the last. At a given boat speed and course length, a boat course traverse time is a constant. Such timing is accomplished by having a person on each boat start a hand-held stopwatch when the boat passes the first buoy and stop the stopwatch when the boat passes the final buoy. Such a methodology, unfortunately, can be subject to substantial variation, primarily due to errors reading the stop-watch on a moving boat.
The accuracy required by the American Water Ski Association (AWSA) for standard tournaments is .+-.1/2 mile/hour and for so-called record-capability tournaments is .+-.1/4 mile/hour. Thus, the benefit of having access to an electronic timer should be evident. The accuracy required, however, by the AWSA for such electronic timing is 0.05/100. That is, for every 100 seconds, the measured time may deviate by no more than 0.05 seconds. As is known by those skilled in the art, a typical boat speed for water skiing competition is 36 miles/hour with a concomitant course traverse time of 16.08 seconds.
Thus, heretofore unknown in the prior art is a convenient and safe method and apparatus for conveniently timing the speed of motor boats in water ski competitions and the like. There have been improvements in the prior art relative to devices for detecting the position of moving bodies on land as well as in aqueous environments. For example, Posseme, in U.S. Pat. No. 4,470,013, discloses a device for the dynamic anchoring of a ship to a platform in the open sea. The Posseme device, improving upon certain techniques disclosed in U.S. Pat. No. 4,316,253, positions a ship using an induced magnetic field resulting from two submerged conductors disposed in the platform through which alternating current passes in opposite directions. The moving ship contains magnetometers which measure the instantaneous induced magnetic field. As another example, in U.S. Pat. No. 4,943,772, Manaupu et al disclose a position sensor for detecting the position of railway vehicle axle relative to a rail of track. The Manaupu sensor provides means for producing magnetic field above the rail with lines of force of the field being vertical and perpendicular to the direction of the axle, and means for measuring the value of the component of the magnetic field in the direction of the axle, whereby the distortion of the magnetic field associated with the rail as approached by the axle is observed via hall-effect probes. More particularly, these two hall-effect probes are secured to the axle with their planes being perpendicular to the axles direction and the value of the component of the magnetic field in the direction of the axle being proportional to this separation being detected. As another example, Paesch et al, in U.S. Pat. No. 4,935,697, disclose a method and apparatus for measuring the flight path of projectile be detecting either an electrical charge imported to the projectile by friction with air and/or gas fumes generated during ignition or detonation, via at least one inductively operated sensor. The resulting signal may be used to measure time of flight, velocity, etc. The Paesch sensor is an improvement over optical measuring methods which are susceptible to the vicissitudes of whether and vary with the amount of light available. The magnetic field is generated by moving charge which produces a voltage in the induction coil of the sensor which is responsive to the velocity of the projectile and may actuate other measuring devices. As still another example of developments in the position sensing art, in U.S. Pat. No. 4,788,498 Uemura discloses a magnetic detector for detecting the position necessary for stopping vehicles, e.g., elevators, trains, etc., at predetermined positions without human intervention. Uemura improved magnetic detector comprises a magnetic field generating substance, pairs of linearly aligned saturable coils, a high-frequency oscillator for supplying high-frequency voltage through resistors to each pair of coils, and means for rectifying these voltages across the resistors in a differential manner as output. By combining the Uemura magnetic detector with a differentiating circuit, a velocity detector embodiment may be used.
Accordingly, these limitations and disadvantages of the prior art are overcome with the present invention, and improved means and techniques are provided which are useful for reliably and conveniently detecting and recording the speed of aquatic vehicles through a water ski course, using signals generated by a magnetic field.